1. Field of the Invention
The present invention relates to a vehicle power unit, the power unit including an internal combustion engine and a transmission, the transmission modifying the rotational speed of the engine and transmitting the rotational driving force of the engine to vehicle wheels.
2. Description of the Background Art
In a known a vehicle power unit, which includes an internal combustion engine and a transmission, the transmission is configured to include input and output shafts disposed parallel to each other, and to further include a plurality of gear trains arranged between the input and output shafts. Such a power unit is disclosed, for example, in Japanese Patent Laid-Open No. 2002-227939. In the known vehicle power unit, lubricating oil is fed to sliding portions such as shafts and gears in order to stably operate an internal combustion engine and a power transmission device. A power unit case, which provides a housing for the internal combustion engine and the power transmission device, is formed with an oil storage portion adapted to collect the lubricating oil, which is fed under pressure to various portions by a feed pump.
The power transmission device of Japanese Patent Laid-Open No. 2002-227939 transmits rotation of a crankshaft to a main shaft, and the rotation of the main shaft to a countershaft in order to set a forward stage, or to an idle shaft for setting a reverse stage. Thus, the rotation of either the counter shaft or idle shaft is transmitted to an output shaft. These shafts are rotated and are provided with gears thereon; therefore, lubricating oil is fed to the shafts and to the gears. The lubricating oil fed to the shafts collects on the bottom of an inner space housed in a gear case housing the power transmission device.
However, the output shaft in the power transmission device of Japanese Patent Laid-Open No. 2002-227939 is disposed below a line connecting the respective shaft centers of the counter shaft and the idle shaft. Therefore, gearwheels carried on a shaft whose height from the oil storage portion is small are met with great stirring resistance, which may possibly lead to deterioration in power transmission efficiency.
In view of such a problem, an object of the present invention is to provide a power transmission device for a vehicle configured to quickly return lubricating oil which has been fed to the power transmission device to an oil storage portion.